Various organic synthetic reactions using metal complexes have hitherto been developed and utilized for many purposes. In particular, there are a number of reports on asymmetric catalysts to be used in asymmetric synthesis, i.e., asymmetric isomerization, asymmetric hydrogenation, and the like. Of the reported asymmetric catalysts, metal complexes formed between metallic rhodium and an optically active tertiary phosphine are especially well known as catalysts for asymmetric hydrogenation. Such complexes typically include a rhodium-phosphine complex using 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as BINAP) as a ligand as disclosed in Japanese Patent Application (OPI) No. 61937/80 (the term "OPI" as used herein means an "unexamined published Japanese patent application").
Inoue et al reports in Chemistry Letters, p. 1007-1008 (1985) that they obtained citronellol by asymmetric hydrogenation of geraniol or nerol using various rhodium-phosphine catalysts in an optical yield of 66%.
Other examples of the ligand include a rhodium-phosphine complex using 2,2'-bis(diphenylphosphino)-6,6'-dimethylbiphenyl as disclosed in Japanese Patent Application (OPI) No. 65051/84.
On the other hand, known ruthenium complexes, though there are not so many reports as compared with rhodium complexes, include those having BINAP or 2,2'-bis(di-p-tolylphosphino)-1,1'-binaphthyl (hereinafter abbreviated as T-BINAP) as a ligand, e.g., Ru.sub.2 Cl.sub.4 (BINAP).sub.2 (NEt.sub.3) (wherein Et represents an ethyl group, hereinafter the same), Ru.sub.2 Cl.sub.4 (T-BINAP).sub.2 (NEt.sub.3), RuHCl(BINAP).sub.2, and RuHCl(T-BINAP).sub.2, as reported in Ikariya et al., J. Chem. Soc., Chem. Commun., p. 922, (1985). However, the state-of-the-art ruthenium complexes are not satisfactory in stability as well as optical yield attained.
Although metallic rhodium provides excellent complex catalysts, it is expensive due to limitations in place and quantity of production. When used as a catalyst component, it forms a large proportion in cost of the catalyst, ultimately resulting in increase in cost of the final commercial products. While metallic ruthenium is cheaper than rhodium and appears promising as a catalyst component for industrial application, it still has problems in its activity to cope with precision reactions and its range of application. Therefore, it has been keenly demanded to develop a catalyst which is inexpensive, has high activity and durability, and catalyzes asymmetric reactions to attain high optical yields, i.e., to produce reaction products having high optical purity.